The invention relates to an electric measuring arrangement having at least one measuring sensor and an evaluation circuit for determining the level of an electrically conductive liquid, such as water, in a container as well as other physical properties thereof.
The known electric measuring arrangement, from which the invention starts, serves only for measurement of the level of a liquid in a container. For this purpose, on the wall of the container a measuring head is placed, whose position corresponds to a specific level of the liquid in the container. If the liquid reaches this measuring head, an output signal is given by the measuring sensor, which is evaluated by the evaluation circuit as "reaching of the level." The measuring sensor is designed as a capacitively operating, contactless actuatable proximity switch. However, it can also be a measuring sensor, which works with two measuring electrodes, which are then bridged by the electrically conductive liquid.
The known electric measuring arrangement, explained above, from experience, has proved itself in principle but suffers from the disadvantage that only a discrete measurement is possible. Moreover, it would be advantageous to be able to observe more extensive measurements.
Additionally, stray field sensors for the measurement of the electrolytic conductivity of a liquid have long been known, by themselves (cf. "messen +prufen/automatik", Oct. 1976, 554, 563). Therefore, reference is made to the above-mentioned technical literature for the theory and measuring technology of stray field sensors. It is essential that a measuring sensor designed as a stray field sensor definitely be able to have four or six measuring electrodes, keeping in mind that, for reasons of measuring technique, it is suitable to separate the current electrodes from the voltage electrodes for the potential measurement. As a result the polarization effects on the electrodes through which the current flows are outside the actual measuring range of the voltage electrodes.